Hot Rods How to Build a 250+ mph 1929 Model A Roadster

Great thread! Good job! Congratulations!

 

Yes, the reason for destroking the crank is to get the engine size down to fit in the D cl***, where there was a lower speed record. That said, it was obviously a very tough record because it stood for 45 years, and I’m not the first guy to try to break it. Before the Temple’s set their record in ‘81 it was set by Al Teague in the Sadd, Teague, Bentley roadster in 1970. Those were two serious roadsters…all time greats.

If we would have used the stock 3.906” stroke of a ‘57-58 Chrysler 392 we would be in the “B” category. The 911 Roadster currently holds that record and all the BFR records above us. I’m not ready to tackle those yet. Baby steps, lol.

The engine is designed to turn 7000 rpm. We have it geared right now to where it is only turning about 5750 to go 250 mph. It honestly could use a higher gear because it makes so much torque. The engine doesn’t seem to know that it’s missing an inch of stroke.

For a long time the general consensus was that roadsters liked 60 rear/ 40 front for weight distribution. But in the modern era that sentiment is changing a little because roadsters are going faster and the course (salt) is not what it used to be.

I’ve actually experimented with weight bias in my car, and found that it likes more weight/ ballast in the nose. Part of the reason for that is probably due to the weight of fuel that we are burning during a run. Part of it is due to the CG needing to be ahead of the CP for stability.

One of the things that has been discovered is that a ‘28-29 roadster generates some lift at the rear when you get into the mid-200 range, and it gets worse up closer to 300. The CG starts moving rearwards as the speed gets higher and the lift increases…therefore it might make sense to have weight bias shifted further forward to counteract that problem.

There is also an aero wall that you have to drive through to get to those speeds, and that just takes brute power. The car has to be heavy to stay planted, because roadsters can’t use any wings or aero devices.

And to your point about weight loss from burning fuel, we lost about 260 pounds of m*** over the front axle during the back-up run. Nitro weighs approx. 9.5 lbs per gallon.

 

Thanks for posting all this. .
Congrats on the records.
The Sadd, Teague, Bentley roadster is my favorite Fuel roadster. Yours is the new one. .
Marcus...

 

Yeah, I kind of figured that was part of it too. I understand that idea of learning and growing, but treading where no man has gone before on fuel (congrats!) is not exactly baby steps! More like tiptoeing in no man's land.

Again, armchair quarterbacking here with no experience. But I've heard nitro loves being loaded down on the strip.
How that relates to minutes of WOT and going thru weight changes and thermal stuff that is starting to get into SR-71 levels is where those baby steps make sense.
Thanks for answering spectator foolishness.

 

Amazing talent in all respects, from the drawing, to the fab, welding, mechanics, paint, driving and also presenting the do***ented journey to all of us.

 

Thanks for sharing the details of the build and the trials and tribulations of working to get the record.
I got to watch the run that called for "take it to impound" on you Tube.

 

That is true, a nitro engine thrives under load.

When you can get it loaded down and can keep pushing fuel into the combustion chamber, that’s when a nitro engine will make the most power…as long as you have a hot enough spark to ignite it.

With that comes a caveat…we can only carry so much fuel in a roadster, so we have to walk a fine line with the tune-up, rear gear, and resulting RPM. When you load the engine and it’s making power it wants more fuel. Put more timing in it’s probably gonna want more fuel. When you turn more RPM the fuel pump spins faster and pumps more fuel. The longer you stay on course, the more fuel you need. That’s why the 911 roadster couldn’t go to the 5 mile timer. It always got it done by the 3 or 4, which is impressive.

It’s really pretty incredible that any blown fuel engine lasts for 5 miles with the throttle wide open. Much less 10 miles to back up a record. The stresses on the parts are ridiculous.

 

Great read, and success! Congrats to you and the team! But, we all know it takes some change and then some to do what you're doing, and then DO IT! Hat's off to you!

 

Thanks for doing this.....Very interesting road to get there....

 

Awesome! Thanks for taking us along.

 

Brian @B*** -

Awesome thread! . . . So glad you posted it! . . . Much appreciated!

Congrats again to you (and the whole B***, DeRuvo, & Eshenbaugh team) on the new D/BFR record . . . what a great achievement!​

- Todd @HEMI32 Olson

 

When you are in a spin over 220 mph do you try and correct it or let the car correct itself, great thread been a fan of your work for years.

 

Are you allowed any engine repairs in impound if you hurt it on the first p***?

 

I have only spun the car the one time, and that was last year’s Speedweek at 176 mph. You would think it would’ve been because the rear tires lost traction, but that’s not what the data showed. The data showed that the front end got “light” and the rear tires drove it around in a circle as it “snap” spun.

I accidentally took off in 2nd gear on that p***, and when I realized that, I left it in second gear too long before shifting to high gear. The car makes so much power above 5000 rpm that it literally lifted the front axle and unsettled the balance enough to spin the car. Above 200 mph it doesn’t seem to have this problem…I’m still not totally sure why…but I suspect it’s the rate of acceleration. It rocketed from 150 mph to 176 mph in just a couple of seconds before that spin.

From that data, I added more ballast to the front axle, and decided to short shift the car a little sooner into high gear. (And to make absolutely sure I didn’t accidentally hit a shift ****on getting in the car.)

When the car spun, there was no getting it back. It happened instantaneously, even though it kind of felt like it was in slow motion as it came around.

Once I realized it was in a spin, I pulled the fuel shut off and first parachute before it got all the way through the spin…and when the chute bloomed, it pulled the car straight, only making one full revolution. Then it was just rolling down the course, so I pulled the second chute and steered it off the course.

I’d always been scared to spin a car on the salt, and fortunately it didn’t go too badly.

After you spin, you have to have the car re-inspected. I was happy that it didn’t hurt anything on the car during that spin except for some minor rubber loss on one front tire. That made me feel really good about the car’s construction, and my reaction to the spin from the driver's seat.

 

You get 4 hours to service the car in impound. With a nitro engine there is a possibility of hurting parts, so as long as you have the parts to fix it and can get it done in the time allowed, I’m pretty sure you can change whatever is necessary.

 

Wow, what a project! Beautiful and fast! Your work ethic, and attention to detail never cease to amaze, Brian! Sorry if I missed it, but what did it scale-out at, pre/post fuel?

 

Thanks! You’re right, I didn’t talk about what the car weighs. I’m always making changes to the weight and distribution, so it’s not a simple answer.

It’s a heavy car. You need weight in the roadster cl*** to keep the car planted to the ground.

When I built the car, I built it as heavy as I could without any ballast. It came out around 3500 lbs fully fueled with me in it the first year, and I had no ballast in it. It drove just fine with the 4-banger, even with the wet conditions of ‘23. But I could tell it wasn’t heavy enough.

I never wanted to add weight just because other guys told me I needed to. That wasn’t because I was stubborn…I wanted to feel what the car felt like and add more weight as necessary. Yes, I ultimately did have to make it heavier, but I wanted to know that it needed it and why.

The second year I added about 300 lbs to the car, and it weighed a little over 3800 lbs wet with me in it. It drove like a dream up to a record of 212 mph. Never felt unsettled.

Then when I put the blown V8 in it I knew it was going to have to be heavier. So it weighed about 4700 lbs wet with me in it last year. Data showed the front was too light, and I had Tom Burkland help me with figuring out where the CG and CP are.

So this year I added ballast to the nose, and the car weighed a little over 4900 lbs wet with me in it. We carry about 330 lbs of fuel, and I weigh about 215 plus about 15-20 lbs of gear…so it’s a little over 4300 dry.

I just picked up some lead to add more weight for next year. It will probably weigh around 5700-5800 next year. I still don’t know if that’s heavy enough.

 

This opens the eyes to the thinking of lighter is faster (true) in most racing scenarios. When the forces of nature enter the game, it changes! I figured it was a tank from the build photo's, but damn!
Thanks for the explanations Brian, I'm sure we all appreciate the hell out of you taking the time!

 

where do you find room in that tight package for that much weight?

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@BigJoeArt , I did a search, AI answered but I don't like that. Here's an image of 1K lead.

 

I have resisted filling the frame rails with lead shot until now, but I think it’s time.

 

This reminded me of a late family friend from Montana who home-built and campaigned a streamliner at Speed Week in the early 2000's. He was a very smart and talented home fabricator with a lot of trick stuff on the car, but not an engineer.

His observation was that roadsters got light in the rear and wanted to spin in the high 200's, most likely due significantly to the condition you mentioned as a result of low pressure at the rear of the car creating lift at that speed. He mentioned several times during downtime at Bonneville that his idea was to build a roadster with the body mounted backwards to combat it. I'm not sure what cl*** he thought such a contraption would fit into, but I think it kind of glossed over the science of what's actually happening to the air at speed. Nevertheless, I still chuckle once in a while at the prospect of a roadster going down the course backwards at Bonneville in an attempt to combat the aerodynamic issues inherent in the original vehicle design.

 

I'm curious about the solid-mounted rear axle on your roadster. Does the downforce at speed help keep the rear planted and therefore no suspension is needed? Is there any special reason why it works so well?

 

I wondered if you had done that yet.
are they 2x6x.250?
1.5(ID)x5.5(ID)x140=1155CI per foot x .41 pounds for lead shot = 40.59 Lb's per foot, or 473.55 per rail.

I think your rails are wedge cut, so It would be less, but there's likely 800 pounds available there.

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Yes, that is correct. That is also what I figured I would get by filling them full of lead shot...around 800 lbs. My friend and fellow 2-club member Vince Norton has a similar frame under his roadster, and he got 800 lbs by filling his rails with shot.

Shouldn't change the front/rear weight bias much either. But I should be able to add a bit more ballast to the front if I need to, due to the taper of the rails.

 

This relies a lot on "tribal knowledge", but the solid rear axle just seems to work well in a roadster.

All the fastest roadsters (with the exception of Doug Robinson's yellow BMR Roadster) have got it done with no rear suspension. The reason is most likely that it's a carry over from drag racing, where fuel cars don't run rear suspension.

This is a little bit of personal opinion and/or unproven theory...but if you look at suspension cycle over the length of a 5 mile run at 250 mph on a smooth course, the spring really isn't going to be doing all that much. There just isn't enough rebound recovery time from bump to bump if the car is heavy enough to stay planted. If you did decide to have rear suspension in a fast roadster, I would think that you wouldn't need much up/down travel.

The other advantage that I personally took into consideration was how much easier it would be to build the car rigid in the rear. It simplifies an already complex car by taking rear suspension tuning out of the equation. Also reduces the chance of rear axle failure by removing some of the shock load from the pinion.

I can also tell you that you do not notice the lack of rear suspension when driving the car. Even on a course as rough as what we had this year for Speedweek. Part of that could be that I'm used to driving sketchy old hot rods on the terrible streets of Dallas, but I digress...

 

Thanks for the additional insight.

 

I'm curious about the spark plugs on the left "bank" of the 4 cyl. Are the just there to balance the esthetics a bit, or do they have some mysterious function.

 

This is absolutely fascinating!! Thank you for posting!